Approaches to the determination of the worst-case available output power or induced voltage in a structure acting as an unintended receiving antenna are presented. Electrically-large structures have complex radiation patterns and a relatively high efficiency. The most realistic canonical model for unintended receiving antennas is the loop antenna, but when this becomes electrically-large its radiation pattern becomes difficult to predict. However, it is known that the pattern will be similar to that of the long dipole antenna and, since inefficiency effects are not significant in this case, it is acceptable to use the long dipole as the canonical model for the electrically-large case. An algorithm for computation of long dipole characteristics was developed: computed worstcase results are presented.The results have implications for prediction of the following hazards: ignition of flammable gas mixtures; shock/burn hazards to personnel; initiation of electric detonators.